Compressor unloader



S. B. REDFIELD.

COMPRESSOR UNLOADER.

APPLICATION FILED JAN. 17, 1921.

1,421,309,, Patented. June 27, 1922.

H IM A H R fi v T L a? l g I @Z 19 w INVENTOR unrrso STATES OFFEQE.

SNOWDEN B. REDFIELD. OF EASTON. PENNSYLVANIA. ASSIGNOR TO INGERSOLL- RAND COMPANY, 03 JERSEY CITY, NEW JERSEY, A CORPORATION OF NEW JERSEY.

COMPRESSOR UNLOADER.

Specification of Letters Patent. Patented June 27, 1922.

Application filed January 17, 1921. Serial No. M7388.

To all cola-0mz't mar concern:

lie it known that Snowmen B. RnorInLn, a citizen of the United States. a resident of Easton. Northampton County, and State of Pennsylvania, have invented certain new and useful Im. rovements in Compressor l nloaders. of which the following is a specitication.

This invention relates to starting unloaders for compressors and the primary object oi the invention is to secure a definite time element between the starting and loading of the compressor. The device is particularly applicable to a compiessor in which the starting and stopping of the motor driving the compressor is controlled by electrical or other suitable and usual means, so that the function of my unloader is primarily to provide for unloading during the starting period.

Another important object of the invention is to enable the said time element on starting to be varied and controlled as desired. depending upon the size of the compressor and other factors which may enter into the construction of the unit.

To these and other ends, which will hereinafter appear. the invention consists of the apparatus shown in one of its preferred forms in the accompanying drawings, in which- Figure 1 is a longitudinal sectional elevation of the unloader. and

Figure 2 is a diagrammatic elevation partly in vertical section of the unloader up )lied to a compressor unit.

iteterring to the drawings, and at first more particularly to Figure 2, the unloader A is adapted to be connected in the discharge line B of acompressor C between the compressor and the usual receiver tank D. The compressor may be of any suitable type. in this instance, the parts being shown iliagranunatically, and comprising a cylinder E and reciprocatory piston F adapted to be driven from any suitable source of power. The compressor is rovided with the inlet valves (3 and the (ischarge valves H, the discharge chamber J of the compressor being connected to the discharge line B.

Referring more particularly to the details of the unloader as shown in Figure l, the unloader comprises a suitable valve casing K having the main chamber L separated from the outlet 0 of the valve casin b the partition P on which the main 5160i; valve Q is adapted to be seated for controlling the dischar e from the valve casing. The check valve is provided with a spring I bearing on the valve and held by the ca 5. The pressure in the receiver tank l normally holds the check valve Q to its seat.

The wall T of the main chamber L is provided with a valve seat U on which a relief valve V is adaited to seat. The extension W of this relie valve is preferably adapted to bear against the main check valve Q, forming a stop. The relief valve V controls a vent X atl'ording communication between the main valve chamber and the atmosphere.

The stem Y of the relief valve V is shown provided with the time element piston Z operating in a chamber formed by theextension a of the main valve casing K. Pressure means which may be in the form of a comparatively heavy spring I) cooperates with the time element piston Z and is adapted to be compressed between said piston and the cap 0 on the end of an adjustable set screw d extendin through the extension at. The spring I) ten s to hold the relief valve V in open position as indicated in Figure 1, and is opposed b the pressure on the time element piston Z uilt up in the main chamber L of the valve casing.

In the operation 01 the unloader so far described let it be assumed that the compressor is standing, that is, not running, in which case the main check valve Q will be closed with perhaps one hundred pounds pressure above it, due to the pressure in the discharge tank D. The relief valve V is held in open position b means of the heavy spring 6 under the time element piston Z. Assume then, that the motor or other source of power driving the compressor starts up slowly, in which case the air from the discharge line B passes out of the unloader valve casing K under the relie valve V and through the atmospheric vent X. The vent X is preferably of such size that if the compressor were running at full speed. the pressure required to pass all of tie air from the compressor through the vent X. would be a certain definite figure,

. desired time element.

as for instance fifteen pounds, which n'ay be taken as an example, and this isonly after full speed has been attained.

The set screw d for the time element piston spring I) is so adjusted that when the pressure in the main chamber L of the valve casing, sli htly throttled by the opening of the vent reaches a certain pressure less than fifteen pounds, as for instance eight pounds, as an illustrative example, the time element piston Z will be depressed and the relief valve V will be closed. After this op eration occurs, the air from the compressor will build u the compression in the discharge pipe and in the main chamber L of the valve casing until the pressure slightly exceeds the pressure in the discharge tank D, causing the main check valve Q, to open, in-

" dicating that the compressor hastaken up its load.

I am enabled to ad'ust the set screw (i so that the relief valve will close after any In describing the op eration of the apparatus so far disclosed, fifteen was selected as the number of pounds pressure required to pass the air from the compressor at full speed through the atmospheric vent X and in actual practice, the set screw (2 has been set so that the time element piston Z will be depressed at eight pounds pressure in the main chamber L. Under these conditions, if the piston Z for any rea son should stick and should not be depressed at eight pounds pressure. the pressure in the unloader will automatically build up to fifteen pounds giving practically 100% greater pressure available to force the iston Z downward in case it should stick. he time element piston Z can also be adjusted to move downward at as low or as high a pressure as may be required, to ive the desired time element on starting. n adjustment for eight pounds pressure on the piston 'Z has been found to give about ten seconds starting time on the unit to which the unloader was applied, and one of the advantages of my construction is the appreciable pressure range obtainable with the adjustment of the set screw afor the time element piston spring I).

When the pressure in the discharge tank D has reached a certain maximum, as for instance one hundred and fifty pounds, the usual. electrical controller or other device provided for this purpose will stop the motor driving the compressor and under these conditions, the check valve Q will automatically close. Another important feature of my construction relates to automatic means for relieving the pressure remaining in the main valve casing upon stopping and before re-starting the compressor. I provide means for allowing the air in the chamber L of the valve casing and in the discharge pipe from the compressor to exhaust to atmosphere through a connection 0 from the main valve chamber and through the atmospherid- 'ivent space of not'over a ew seconds, depending upon the pressure and the size of the discharge pipe. When the check valve Q, is in open position, and the compressor is'pumping into the tank D, the small bleeder vent f is maintained closed, as will be described so that there is no leak to atmosphere during such time.

In order to bleed the air trapped in the piping B between the com ressor discharge and the main check valve & of the starting unloader A, when the compressor has stopped, the tube e is bled from a vent in the body ofthe starting unloader under or on the inlet side of the main check valve Q. This tube 6 leads to one end, in this instance, the bottom of the automatic" bleeder 9 ,shown in the drawin s. The air coming through the bleeder tu e e, enters the lower body portion of the automatic bleeder g and will pass out to atmosphere through the vent f except when the needle valve k is pressed C and a check valve 9 is held to its seat in' the bleeder by the relatively light spring 7". The underlying principles upon which the operation of this automatic bleeder is based, are substantially as follows :--When a compressor piston, as the piston F comes to rest, it automatically seeks some intermediate position in the cylinder C due to the expansion of the air behind it, until the pressures on the two sides of the piston are approximately equal. Owing to the fact that the air on the suction side of the piston at the time of stopping will be approximately atmospheric, the air on the other side of the piston will expand and move the piston, compressing the air on the suction side slightly until the pressure of the expanded air becomes very nearly the same as the pressure of the air trapped on the suction side. Experiment has proved that with atmospheric intake, and intake valves which are commercially perfectly, tight, the pressure left inside the compressor cylinder is very low relative to the discharge pressure of the machine.

Applying these principles to the apparatus illustrated, a little air enters the small space t in the upper part of the body of the bleeder g by means of the check valve 9 during the discharge period of the compressor stroke. This pressure will be apdown the diaphragm y, closing the needle valve h and preventing thebleeding .of the starting unloader through the tube .6 and vent f. v,

- A very small vents is preferably provided in the check valve q but this vent-sis not large enough to allow the pressure in the space t above the diaphragm j to drop sufii ciently during the suction stroke at that end of the compressing cylinder to permit the needle valve h to open. Thus, ,during the entire-run of the compressor, the diaphragm j is held down, closing the needle valve h and preventing the bleeding of. the unloader A through the tube andthe vent f.

As the compressor stops, the piston F will seek some intermediate position not far from mid stroke, as before describedand'the compressor cylinder pressure Will be relatively low. This being the case and the compressor- F being at rest, the very small .amount of air in the space 2? above the diaphragm y' bleeds through the vent 8 into the compressor cylinder C1 This allows the spring to force the diaphragm j upward,

"Opens the needle valve in and allows the air in the chamber L of the unloader A to bleed back through the tube e and the vent f, so that the pressure in the compressor di charge pipe 13 between the compressor and the unloader is bled to atmosphere. When this pressure has lowered sufficiently to allow the spring I) of the time element piston Z of the starting unloader to raise the piston and open the relief valve V, the unloader is in condition to start the compressor and ready to permit the passage of the air to atmosphere through the side outlet or vent X of the unloader, as hereinbefore' described.

Upon re-starting the compressor, the

building up of the discharge pressure opens the needle valve h, shutting ofi' the bleeding tube 6 leading from the unloader, and the machine proceeds to do its .normal work of filling the receiver.

By means of this automatic bleeder, the unloading and re-loading of the compressor is entirely independent of the electrlcal or other apparatus used for starting and driving the compressor and is controlled only by the pressure in the compressor cylinder or the speed of the compressor piston. In this way, in case the electrical current should fail, the machine is immediately unloaded and the motor protected against the possibility of starting the machine against air pressure. A

It would be possible to place vent 8 somewhere in the body g of the bleeder or even in the diaphragm j, but in that case, the;

leakage through this vent 8 would be con-f occur during the time that the check valve 9 is on its seat, which is during the. suction stroke of the piston for that end of the compressor; a

I claim: I

1. A compressor unloader, comprising a main valve casing adapted to be connected in the discharge line of a compressor, a main discharge valve controlling the outlet from sald casing to the discharge line, a vent to atmosphere from said casing, automatic means for preventing the opening of said main discharge valve until the compressor has attained suflicient speed to permit the load to be safely thrown on the compressor and automatic means controlled by the pressure in the compressor cylinder for relieving the pressure remaining in the main valve casing as the compressor comes to a stop.

2. A compressor unloader, comprising a main valve casing adapted to be connected in the discharge line of a compressor, a main discharge valve controlling the outlet from said casing tothe discharge line, a vent to atmosphere from said casing, automatic means for producing a delayed time element between the starting of the compressor and the opening of said main discharge valve and automatic means controlled by the pressure in the compressor cylinder for relieving the pressure remaining in the main valve casin as the compressor comes to a stop.

3. compressor unloader, comprising a main valve casing adapted to'be connected in the discharge line of a compressor, a main discharge valve controlling the outlet from said casing to the discharge line, a vent to atmosphere from said casing, an automatic relief valve in said casing controlling said vent to atmosphere, for preventing the 'loading of the compressor until an element of time has elapsed after starting and automatic means controlled by the pressure in the compressor cylinder for relieving the pressure remaining in the main valve casing as the compressor comes to a stop.

4. A compressor unloader, comprising a main valve casing, adapted to be connected in the discharge line of a compressor, a main discharge valve controlling the outlet from said casing to the discharge line, a vent to atmosphere from said casing, an'automatic relief valve in said casing controlling said vent to atmosphere, said relief valve automatically closing before the main valve opens on starting of the compressor, and opening after the main discharge valve closes when the compressor stops and automatic means controlled by the pressure in the sure remaining in the main valve casing as the compressor comes to a stop.

5. A compressor unloadcr, comprising a valve casing having a main valve chamber adapted to be connected in the discharge line of a compressor, a main check valve con trolling the outlet 'of said chamber to the discharge line, a relief valve controlling an atmospheric vent from said main chamber, a pressure actuated piston connected to said relief valve, subject to the pressure in the main chamber and to opposing pressure means, whereby the load is not thrown on the compressor until ithas reached a speed sutiicient to build up enough pressure in the said main chamber to overcome the opposing pressure means of the relief valve and close the said relief valve and automatic means controlled by the pressure in the compressor cylinder for relieving the pressure remaining in the main valve casing as the compressor comes to a stop.

6. An unloader for compressors, comprising a valve casing adapted to be connected in the discharge line of a compressor and having a main valve chamber, a main check valve controlling the discharge outlet from the said casing. an auxiliary relief valve controlling an atmospheric vent from said main chamber, a piston connected to the stem of said relief valve subjectto the pressure in the main chamber tending to close the relief valve and opposed by an adjustable spring tending to open the relief valve, an auxiliary blceder valve, a connection from the main valve chamber to said auxiliary bleeder valve. said bleeder valve being controlled by the pressure in the compressor cylinder, whereby the pressure remaining in the main valve casing is relieved before the re-starting of the compressor. and the main check valve will not be open to load the compressor until the relief valve has closed, due to the buildingup of a predetermined pressure in the said main chamber of the casing.

7. An unloader for compressors, comprising a valve casing having an inlet adapted to be connected to the discharge of a compressor and an outlet adapted to be connected to a receiver tank. a main discharge valve chamber in said casing, a spring pressed main check valve controlling communication between said main chamber and the outlet of the casing, a relief valve controlling a vent from said main chamber to atmosphere, a time element piston connected to the stem of said relief valve. an adjustable spring cooperating with said piston and tending to open said relief valve, an auxiliary bleeder valve, a connection from said main valve chamber to the said auxiliary bleeder valve, said bleeder valve being controlled by the pressure in the compressor cylinder, whereby the pressure remaining in the main valve casing is relieved before the re-starting of the compressor and a delayed time element is provided between the starting and loading of the compressor due to the successive operation of the relief valve and main check valve.

8. An unloader t'or compressors comprising a main valve casing adapted to be connected in the discharge line of a compressor, a main discharge valve controlling the outlet from said casing to the discharge line, automatic means for producing a time element between the starting of the compressor and the opening of said main check valve, and automatic means controlled by the speed of the compressor piston for relieving the pressure remaining in the main valve casing as the compressor comes to a stop;

9. An unloader for compressors, comprising a valve casing adapted to be connected in the discharge line of a compressor, a main discharge valve controlling the outlet from said casing to the discharge line, and operative means connected to said valve casing for automatically unloading and re-loading the compressor controlled only by the speed of the compressor piston.

10. An unloader for compressors comprising a main valve casing adapted to be connected in the discharge line of a compressor, a main discharge valve controlling the outlet from said casing to the discharge line, automatic means for producing a time element between the starting of the compressor and the opening of said main check valve, and automatic means controlled by the pressure in the compressor cylinder for relieving the pressure remaining in the main valve casing as the compressor comes to a stop.

11. An unloader for compressors, comprising a main valve casing adapted to be connected in the discharge line of a compressor, a main discharge valve controlling the out let from said casing to the discharge line, and operative means connected to said valve casing for automatically unloading and reloading the compressor controlled only by the pressure in the compressor cylinder.

12. An unloader for compressors comprising a main valve casing adapted to be connected in the discharge line of a compressor, a main discharge valve controlling the outlet from said casing to the discharge line, and automatic means controlled by the pressure in the compressor cylinder for relieving the pressure remaining in the vmain valve casing as the compressor comes to a stop.

13. An unloader for compressors comprising a main valve casing adapted to be connected in the discharge line of a compressor,

tling the outlet of said chamber to the discharge line, a relief valve controlling an atmospheric vent from said main chamber, and a piston connected to said relief valve actuated in one direction by pressure in the main valve chamber and subjected to oppos-- ing pressure means, whereby the load is notthrown on the compressor until it has reached a speed at which the vent to atmosphere from the main valve chamber ceases to be sufiicient to permit the air discharged by the compressor to pam to atmosphere, so that suflicient pressure is built up in the said main chamber to overcome the opposing pressure means of the relief valve and close the said valve, and automatic means controlled by the pressure in the compressor cylinder-for relieving the pressure remaining in the mainvalve casing as the compressor comes to a. stop.

15. An unloader for compressors, comprising a valve casing adapted to be connected in the discharge line of a compressor and having a main valve chamber, a main check valve controlling the discharge outlet from the said casing, an auxiliary relief valve controlling an atmospheric vent from said main chamber, a piston connected to said relief valve and subject to the pressure in the main chamber tending to close the relief valve and opposed by means tending to open the relief valve, an auxiliary bleeder valve, a connection from the main valve chamber to said auxiliary bleeder valve, said bleeder valve'being controlled by the pressure in the compressor cylinder, whereby the pressure remaining in the main valve casing is relieved before the re-starting of the compressor, and the main check valve will not be open to load the compressor until the relief valve has closed, due to the building up of a predetermined pressure in the said main chamber ofthe casing.

16. An unloader for compressors, comprising a valve casing having an inlet adapted to be connected to the discharge of a compressor and an outlet adapted to be connected to a receiver tank, a main discharge valve chamber in said casing, a spring pressed main check valve controlling communication between said main chamber and the outlet of the casing, a relief valve controlling a vent from said chamber to atmosphere. a time element piston connected to said relief valve and-subject to means tending to open the relief valve, an auxiliary bleeder valve, a connection from said main valve chamber to the said auxiliary bleeder valve. said bleeder valve being controlled by the pressure in the compressor cylinder. whereby the pressure remaining in the main valve casing is relieved before the restarting of the compressor and a delayed time element is provided between the starting and loading of the compressor due to the successive operation of the relief valve and main check valve.

In testimony whereof I have signed this specification.

SNOWDEN B. REDFIELD. 

